Semiconductor storage device and method of manufacturing the same

ABSTRACT

A semiconductor storage device includes: memory cells including a transistor and a capacitor; bit lines; word lines; and sense amplifiers including first and second sense amplifiers, wherein the memory cells includes: a first memory cell group sharing a first auxiliary word line; and a second memory cell group sharing a second auxiliary word line, wherein the word lines includes a first word line coupled to the first auxiliary word line and a second word line coupled to the second auxiliary word line, the first word line is coupled to the first auxiliary word line in a first word line contact region, the second word line is coupled to the second auxiliary word line in a second word line contact region, the bit lines includes first and second bit lines coupled to the first sense amplifier on both sides of the first word line contact region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from Japanese PatentApplication No. 2009-248587 filed on Oct. 29, 2009, the entire contentsof which are incorporated herein by reference.

BACKGROUND

1. Field

Embodiments discussed herein relate to a semiconductor storage deviceand a method of manufacturing the semiconductor storage device.

2. Description of Related Art

In a dynamic random access memory (DRAM) cell with the1-transistor/1-capacitor configuration, one current terminal of anaccess transistor is coupled to a bit line, and the other currentterminal of the access transistor is coupled to a storage electrode of acapacitor.

The related art is disclosed in Japanese Laid-open Patent PublicationNo. H11-265995, etc.

SUMMARY

According to one aspect of the embodiments, a semiconductor storagedevice is provided which includes: a semiconductor substrate; aplurality of memory cells formed on the semiconductor substrate, each ofthe memory cells including a transistor and a capacitor; a plurality ofbit lines extending in a first direction; a plurality of word linesextending in a second direction which is different from the firstdirection; and a plurality of sense amplifiers formed in the firstdirection and including first sense amplifiers and second senseamplifiers, wherein the plurality of memory cells includes: a firstmemory cell group sharing a first auxiliary word line extending in thesecond direction as gate electrodes of the transistors; and a secondmemory cell group sharing a second auxiliary word line extending in thesecond direction as gate electrodes of the transistors, wherein theplurality of word lines includes a first word line coupled to the firstauxiliary word line and a second word line coupled to the secondauxiliary word line, the first word line is coupled to the firstauxiliary word line in a first word line contact region which isarranged at one end of the first auxiliary word line, the second wordline being coupled to the second auxiliary word line in a second wordline contact region which is arranged at one end of the second auxiliaryword line, the plurality of bit lines includes a first bit line and asecond bit line respectively provided on both sides of the first wordline contact region, and the first bit line and the second bit line arecoupled to the first sense amplifier.

The object and advantages of the invention will be realized and achievedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an exemplary memory-consolidated logic semiconductordevice.

FIG. 1B illustrates an exemplary memory circuit.

FIG. 1C illustrates an exemplary equivalent circuit.

FIGS. 2A, 2B, 2C and 2D illustrate an exemplary memory cell array and anexemplary memory cell.

FIGS. 3A to 3G illustrate an exemplary process for manufacturing memorycells.

FIGS. 4A to 4L illustrate an exemplary process for manufacturing memorycells.

FIGS. 5A and 5B illustrate an exemplary memory cell array.

FIG. 6 illustrates one example of an exemplary memory cell array.

FIG. 7 illustrates an exemplary equivalent circuit.

FIGS. 8A and 8B illustrate an exemplary memory cell array and anexemplary memory cell.

DESCRIPTION OF EMBODIMENTS

In the figures, dimensions and/or proportions may be exaggerated forclarity of illustration. It will also be understood that when an elementis referred to as being “connected to” another element, it may bedirectly connected or indirectly connected, i.e., intervening elementsmay also be present. Further, it will be understood that when an elementis referred to as being “between” two elements, it may be the onlyelement between the two elements, or one or more intervening elementsmay also be present.

In the dynamic random access memory (DRAM) cell with the1-transistor/1-capacitor configuration, two gate electrodes are arrangedon one active region and three source/drain regions are formed at amiddle and on both the sides, whereby two transistors are formed. Themiddle source/drain region is used as a common bit-line connectionregion and the source/drain regions on both the sides are coupled torespective capacitors, whereby two memory cells are formed. With respectto the memory cells arrayed in a matrix pattern, word lines are arrangedso as to extend in the column direction and bit lines are arranged so asto extend in the row direction, for example.

In the case of open bit lines, two bit lines arranged in differentmemory cell areas are coupled to a sense amplifier. An area of eachmemory cell is reduced, and noise generated in the memory cell area maybe imposed on one of the paired bit lines. In the case of folded bitlines, two bit lines arranged in the same memory cell area are coupledto a sense amplifier. A memory cell to be read is coupled to one bitline, while the other bit line, e.g., a reference bit line, may be notcoupled to the memory cell to be read. An area of each memory cell isincreased, and noise generated in the memory cell area may be imposed onboth of the paired bit lines.

FIG. 1A illustrates an exemplary memory-consolidated logic semiconductordevice. FIG. 1A may be a plan view of a memory-consolidated logicsemiconductor device IC as illustrated in FIG. 1A. Input/output circuitsI/O are arranged in a peripheral portion of the semiconductor device IC.In a central portion of the semiconductor device IC, a logical circuitLG is arranged and memory circuits MG are arranged in a distributed way.

FIG. 1B illustrates an exemplary memory circuit. Sense amplifiers SA andmemory cell groups MCG are arranged on both the sides of a word decoderDC. A second amplifier AM and an input/output address controller I/O•ADCare arranged at one end, e.g., a lower end as viewed on the drawing, ofthe word decoder DC.

FIG. 1C illustrates an exemplary equivalent circuit. The equivalentcircuit illustrated in FIG. 1C may be an equivalent circuit of thememory cell groups MCG. A memory cell array is formed with memory cellsMC arrayed in a matrix pattern. Each of the memory cells MC may be a1-transistor/1-capacitor memory cell including one access transistor Trand one capacitor Cap. Each access transistor Tr includes onesource/drain region coupled to a bit line BL and a gate electrode GEcoupled to a word line WL. The capacitor Cap includes a storageelectrode coupled to the other source/drain region of the accesstransistor Tr.

A plurality of word lines WL extend in the vertical direction, e.g., inthe column direction, and are arranged side by side in the horizontaldirection, e.g., in the row direction. A plurality of bit lines BLextend in the horizontal direction and are arranged side by side in thevertical direction. The bit lines are cross-wired before being input tothe sense amplifier S/A, and a bit line BLi and a reference bit line/BLi corresponding to the bit line BLi are coupled to a common senseamplifier S/Ai. The reference bit line may also be referred as the bitline. Each bit line may extend in the horizontal direction except forthe cross-wiring portion.

The memory cell array may be divided into a plurality of areas in thevertical direction, and each area may include four memory cells MC inthe vertical direction. A first area including memory cells MC1 to MC4,which are coupled respectively to bit lines BL1 to BL4, and a secondarea including memory cells /MC4 to /MC1, which are coupled respectivelyto reference bit lines /BL4 to /BL1 corresponding to the bit lines BL4to BL1, may be arranged alternately.

The gate electrode GE for four access transistors Tr arranged within thearea in the vertical direction is formed of a polysilicon film. The gateelectrode GE may be separated by each area. The gate electrodes GE inthe first area and the second area are alternately coupled to two metalword lines, e.g., WL1 and WL2. With the gate electrodes GE separatedbetween the first area and the second area, the memory circuit may havethe folded bit-line configuration. The word line WL is coupled to thegate electrode GE in a word line contact region WC. The word linecontact region WC is disposed at an end of each gate electrode GE.

For example, a memory cell group including the four memory cells MC1 toMC4 shares a gate electrode AW1 serving as, e.g., an auxiliary wordline, which extends in the vertical direction. Another memory cell groupadjacently positioned above the above-mentioned memory cell group sharesanother gate electrode AW2 serving as, e.g., an auxiliary word line,which extends in the vertical direction. The auxiliary word line AW1 iscoupled to the word line WL1 in a word line contact region WC1 that isdisposed at one end, e.g., a lower end, of the auxiliary word line AW1.The auxiliary word line AW2 is coupled to the word line WL2 in a wordline contact region WC2 that is disposed at one end, e.g., a lower end,of the auxiliary word line AW2. The auxiliary word line AW3 is coupledto the word line WL3 in a word line contact region WC3 that is disposedat one end, e.g., a higher end, of the auxiliary word line AW3. Theauxiliary word line AW4 is coupled to the word line WL4 in a word linecontact region WC4 that is disposed at one end, e.g., a higher end, ofthe auxiliary word line AW4.

Two bit lines adjacent to each other in a sandwiching relation withrespect to the word line contact region WC includes a pair of bit lineBLi and reference bit line /BLi, and they are coupled to a common senseamplifier S/Ai. For example, the bit line BL4 and the reference bit line/BL4 are adjacent to each other in a sandwiching relation with respectto the word line contact region WC1 and are coupled to a common senseamplifier S/A4.

The two bit lines adjacent to each other in a sandwiching relation withrespect to the word line contact region WC may be susceptible to aninfluence of noise caused by voltage changes in the word line contactregion WC. Because the bit line BLi and the corresponding reference bitline /BLi are subjected to substantially the same noise, a noiseinfluence upon a voltage difference between the bit line BLi and thecorresponding reference bit line /BLi may be reduced. Therefore, noisegenerated in the sensing operation may be reduced.

FIGS. 2A, 2B, 2C and 2D illustrate an exemplary memory cell array. FIG.2A illustrates the layout of the memory cell array as viewed from above.FIG. 2B illustrates part of the layout of the memory cell array asviewed from above. A plurality of elongate active regions AR arearranged in a matrix pattern. The active regions AR are arranged suchthat the lengthwise direction of each active region AR is oriented inthe horizontal direction, e.g., in the row direction, and the activeregions AR are arrayed side by side in the vertical direction, e.g., inthe column direction, while their horizontal positions are aligned withone another. Columns of the active regions AR are arrayed side by sidein the row direction. Vertical positions of the active regions ARarrayed side by side in the row direction are aligned with one another.

Each of the active regions AR includes a bit line contact region BCarranged at a center thereof and memory cells MC which are arranged onboth the sides of the bit line contact region BC and each of which has atransistor (portion) Tr and a capacitor (portion) Cap. Transistor gateelectrodes GE are arranged on both the sides of the bit line contactregions BC, thereby forming the transistors Tr in areas where the gateelectrodes GE intersect the active regions AR. Four transistors arrayedside by side in the vertical direction are continuously formed by eachof the gate electrodes GE. Each gate electrode GE has the word linecontact region WC at one end thereof in the vertical direction.

The word line contact regions WC are disposed at one end of the gateelectrode GE positioned on one side of the bit line contact region BCand at one end of the gate electrode GE positioned on the other side ofthe bit line contact region BC. For example, a memory cell groupincluding the memory cells MC1 to MC4 and four memory cells, which arearranged on the side opposed to the memory cells MC1 to MC4 with respectto the bit line contact region BC, shares a gate electrode AW3′ (FIG.2A) serving as, e.g., an auxiliary word line. The word line contactregion WC located on the auxiliary word line AW1 shared by the memorycell group is disposed at a lower end of the auxiliary word line AW1.The word line contact region WC located on the auxiliary word line AW3′is disposed at an upper end of the auxiliary word line AW3′.

Because of the repeated structure in the horizontal direction, a wordline structure coupled to the auxiliary word line AW3′ may besubstantially the same as or similar to the structure, illustrated inFIG. 1C, of a word line WL3 coupled to an auxiliary word line AW3. InFIG. 1C, the auxiliary word line AW3 is coupled to the word line WL3 ina word line contact region WC3 that is disposed at an upper end of theauxiliary word line AW3.

A pitch between adjacent areas in the vertical direction each of whichis included in a different memory cell group, for example, a pitchbetween the active region AR of the memory cell MC4 at a lower end ofthe memory cell group including the memory cells MC1 to MC4 and theactive region AR of the memory cell /MC4 at an upper end of anothermemory cell group that is adjacently positioned under theabove-mentioned memory cell group may be separated by the gateelectrodes GE. For that reason, the word line contact region WC may bedisposed in the above-mentioned pitch. Within each area, e.g., withineach memory cell group, the active regions AR may be arrayed at asubstantially constant pitch, e.g., a minimum pitch, in the verticaldirection such that the memory cells may be arrayed at a high density.

An opposite electrode CE of the capacitor portion Cap is formed so as tooverlap with respective ends of two adjacent columns of active regions.The capacitor portions Cap of the memory cells MC arranged on one sideof one column of active regions and the capacitor portions Cap of thememory cells MC arranged on the other side of another column of activeregions, which is adjacent to the active regions, share the oppositeelectrode CE.

FIG. 2B is a plan view of two memory cells arrayed side by side in thecolumn direction. FIG. 2B illustrates substantially a half of the activeregion AR in the lengthwise direction thereof, e.g., a part of theactive region AR ranging from the bit line contact region BC at a centerto one end of the active region AR. FIG. 2C illustrates a cross-sectionof the active region taken along a line IIC-IIC in FIG. 2B. FIG. 2Dillustrates a cross-section of the capacitor portion taken along a lineIID-IID in FIG. 2B.

As illustrated in FIG. 2C, the bit line contact region BC may be onen-type (or p-type in a p-type cell) diffusion region formedsubstantially at a center of a p-type (or n-type in the p-type cell)active regions AR, which is formed on a silicon substrate 1.

A gate insulating film 3 t is formed on the right side of the bit linecontact region BC. A gate electrode 4 t is formed on the gate insulatingfilm 3 t. The other n-type (or p-type in the p-type cell) diffusionregion 7 is coupled to the capacitor on the right side of an insulatinggate electrode that includes both the gate insulating film 3 t and thegate electrode 4 t.

N-type (or p-type in the p-type cell) impurities are ion-implanted intothe active regions on both the sides of the insulating gate electrode,thereby forming a bit line contact-side extension (diffusion region) 5and a capacitor-side extension (diffusion region) 7. A sidewall spacer 6t is formed on a sidewall of the gate electrode 4 t, and an insulatingfilm 6 c covering the capacitor-side extension 7 is formed. The bit linecontact region BC having low resistance is formed by subsequent ionimplantation.

A capacitor dielectric film 3 c and an opposite electrode 4 c arearranged on one side of the capacitor-side diffusion region 7 opposed tothe gate electrode 4 t. A silicide region 8 including Co—Si or Ni—Si maybe formed on the bit line contact region BC, the gate electrode 4 t, andthe opposite electrode 4 c. A lower interlayer insulating film 9covering the memory cell is deposited and a contact hole is formed byetching to expose the bit line contact region BC. An electricallyconductive plug 10, e.g., a tungsten plug, is buried in the contacthole.

As illustrated in FIG. 2D, trenches are formed around the active regionsAR, and insulating films 2 for the shallow trench isolation (STI)structure are buried in the trenches. In the capacitor region, the STIinsulating films 2 are etched back such that each STI insulating film 2remains in a certain thickness at the bottom of the trench and a recessis formed so as to expose sidewalls of each active region. The capacitordielectric film 3 c is formed on surfaces of the active regions andsidewalls of the active regions, which are exposed to the recesses. Theopposite electrode 4 c is formed on the capacitor dielectric film 3 c.The silicide layer 8 is formed on a surface of the opposite electrode 4c. In the capacitor portion, when a voltage for turning-on a transistoris applied to the opposite electrode 4 c, a channel is induced togenerate a capacitance between the channel and the opposite electrode.

FIGS. 3A to 3G illustrate an exemplary process for manufacturing thememory cells. FIGS. 3A to 3G are each a plan view of a semiconductorsubstrate.

In FIG. 3A, an element (device) isolation region ISO for defining theactive regions AR is formed on the semiconductor substrate. Afteretching back a region of the opposite electrode CE, an insulating filmand a polysilicon film are laminated in the etched-back region. Thepolysilicon film is patterned to form the gate electrode GE and theopposite electrode CE. Four transistors are successively formedcorresponding to one gate electrode GE.

As illustrated in FIG. 3B, the lower interlayer insulating film isformed so as to cover the gate electrode GE and the opposite electrodeCE. The lower interlayer insulating film on the bit line contact regionBC and the word line contact region WC is etched to form a bit linecontact hole BCH and a word line contact hole WCH.

As illustrated in FIG. 3C, a first metal wiring layer is formed on thelower interlayer insulating film. The first metal wiring layer ispatterned to form the bit lines BL1 to BL4 and /BL1 to /BL4, which arecoupled the active regions AR in the bit line contact regions BC. Firstword auxiliary wirings WS1 coupled to the word line contact regions WCmay be formed contemporaneously. The bit line BL4 and the reference bitline /BL4 are arranged in a sandwiching relation with respect to theword line contact region WC, e.g., the end of the gate electrode GE.

The first metal wiring layer is formed, for example, by laminating a TiNlayer, an Al layer, and a TiN layer successively. The first metal wiringlayer is patterned by photolithography and dry etching to form the bitlines BL and the first word auxiliary wirings WS1.

As illustrated in FIG. 3D, the bit lines BL and the first word auxiliarywirings WS1 are covered with a first interlayer insulating film. Thefirst interlayer insulating film is etched to form word line contactholes WCH reaching the first word auxiliary wirings WS1, respectively.Those word line contact holes WCH may be formed by a process that issubstantially the same as or similar to the process illustrated in FIG.3B.

As illustrated in FIG. 3E, a second metal wiring layer is formed on thefirst interlayer insulating film. The second metal wiring layer ispatterned to form second word auxiliary wirings WS2 that are coupled tothe first word auxiliary wirings WS1. The second word auxiliary wiringsWS2 are covered with a second interlayer insulating film, which isetched to form word line contact holes WCH reaching the second wordauxiliary wirings WS2, respectively.

As illustrated in FIG. 3F, a third metal wiring layer is formed on thesecond interlayer insulating film. The third metal wiring layer ispatterned to form the word lines WL that are coupled to the second wordauxiliary wirings WS2. The word lines WL are coupled to the gateelectrodes GE of the transistors through two stages of the wordauxiliary wirings WS2 and WS1.

In the equivalent circuit illustrated in FIG. 1C, the bit lines BL andthe reference bit lines /BL are coupled to the sense amplifiers S/Athrough cross-wirings. The cross-wirings may be formed, for example, byutilizing the second metal wiring layer.

As illustrated in FIG. 3G, auxiliary bit lines CW in the second metalwiring layer are formed such that memory cell-side portions BLC andsense amplifier-side portions BLA of the bit lines in the first metalwiring layer are coupled to each other. Thus, the bit-line cross wiringsfor coupling the memory cell-side portions BLC to the sense amplifiersS/A are formed. The bit lines, which are not cross-wired, may bedirectly connected to the sense amplifiers S/A.

FIGS. 4A to 4L illustrate an exemplary process for manufacturing memorycells. FIG. 4A may be the plan view of the memory cells illustrated inFIG. 2B. The memory cells illustrated in FIG. 4A include two activeregions AR arrayed side by side in the vertical direction as viewed onthe drawing, two bit contact regions BC, a gate electrode GE fortransistor portions, and an opposite electrode CE of a capacitorportion. Each of the active regions AR may have a width of, for example,70 nm to 110 nm and a length of, for example, 1000 nm to 2000 nm. Theactive regions AR may be each surrounded by isolation regions ISO of theSTI structure. The size of the STI structure between the active regionsAR in the widthwise direction may be, for example, 70 nm to 110 nm. Thesize of the STI structure between the active regions AR in thelengthwise direction may be, for example, 70 nm to 110 nm. Lines A-A,B-B, and C-C in FIG. 4A represent directions of cross-sectionsillustrated in FIGS. 4B to 4L.

As illustrated in FIG. 4B, the surface of a silicon substrate 1 isthermally oxidized to form a buffer oxide film 21 having a thickness of,for example, 5 nm to 20 nm. On the buffer oxide film 21, a siliconnitride film 22 having a thickness of 50 nm to 200 nm is deposited withthermo-chemical gas-phase deposition (CVD) at 600° C. to 800° C. byusing source gases such as a silane-based gas and ammonia. In thisstage, the entirety of the silicon substrate may have substantially thesame or similar structure.

As illustrated in FIG. 4C, a resist pattern RP1 corresponding to theform of the active regions AR are formed on the silicon nitride film 22.The silicon nitride film 22 and the silicon oxide film 21 are patternedby dry etching using an etching gas such as tetraflurocarbon (CF₄),thereby forming a hard mask. The resist pattern RP1 may be removed suchthat only the hard disk remains. Dry etching using etching gases such ashydrogen bromide (HBr) and chlorine (Cl₂) are performed on portions ofthe silicon substrate, which are exposed through the hard mask, therebyforming trenches T which have a depth of about 150 nm to 350 nm andwhich surround the active regions AR. The resist pattern may be removed,for example, by using a resist removing liquid or by ashing. Asillustrated in the C-C cross-section of FIG. 4C, the depth of the trenchT may be larger than the width of the active region AR, for example,twice or more than the width of the active region AR.

As illustrated in FIG. 4D, a silicon oxide film liner 23 having athickness of about 2 nm to 10 nm may be formed, as required, on theexposed silicon surface by thermal oxidation. By a high-density plasma(HDP) CVD using a silane-based gas and oxygen, a HDP silicon oxide filmmay be deposited on the silicon oxide film liner 23. Alternatively, byCVD using tetraethoxysilane (TEOS) and oxygen, a TEOS silicon oxide film(hereinafter referred to simply as a “silicon oxide film 2”) may bedeposited thereon. The trenches are filled back with the deposition.Chemical mechanical polishing (CMP) is performed on the substrate fromabove to expose the silicon nitride film 22 that serves as a CMPstopper. The silicon oxide film liner 23 may be omitted from somedrawings described below.

As illustrated in FIG. 4E, a resist pattern RP2 is formed which has anopening in substantially the same or similar shape as or to that of theopposite electrode CE illustrated in FIG. 4A. The silicon oxide film 2exposed in the opening is etched by using, e.g., hexafluorobutadiene(C₄F₆) as an etching gas such that a part of the silicon oxide film 2having a thickness of 50 nm to 150 nm remains at the bottom for thepurpose of element isolation. Sidewalls of the active regions arethereby exposed. The silicon nitride film 22 may be used as an etchingmask. Thereafter, the resist pattern RP2 may be removed.

As illustrated in FIG. 4F, the silicon nitride film 22 is washed out byboiling in phosphoric acid or in a mixed solution of phosphoric acid andfluoric acid. The silicon oxide film 21 is washed out with dilutedfluoric acid or the above-mentioned mixed solution. The (TEOS) siliconoxide film 2 may be etched and a most part of the silicon oxide film 2may be left.

As illustrated in FIG. 4G, the exposed silicon surface is thermallyoxidized to form a sacrifice silicon oxide film 24 having a thickness of5 nm to 10 nm for the purpose of ion implantation.

As illustrated in FIG. 4H, ion implantation of p-type impurities (orn-type impurities in the p-type cell) is performed into the siliconsubstrate through the sacrifice silicon oxide film 24 a plurality oftimes while acceleration energy is changed, thereby forming a p-typewell PW (or n-type well NW in the p-type cell). Thereafter, thesacrifice silicon oxide film 24 may be removed.

As illustrated in FIG. 4I, the exposed silicon surface is cleaned orthermally oxidized to form a gate oxide film 3 having a thickness ofabout 2 nm to 7 nm. A polycrystalline silicon film 4 having a thicknessof about 70 nm to 150 nm is deposited on the gate oxide film 3 bythermal CVD using a silane-based gas and hydrogen while the substratetemperature is set to 400° C. to 750° C. After depositing amorphoussilicon, crystallizing may be performed with heat treatment.

A resist pattern RP3 corresponding to the shapes of the gate electrodeand the opposite electrode is formed on the polycrystalline silicon film4. The pattern for the opposite electrode may have substantially thesame size as an opening that is used to form a recess for the capacitor.The thickness of the polycrystalline silicon film 4 may be set to such avalue as enough to fill back the trenches T. The polycrystalline siliconfilm 4 is etched with the resist pattern RP3 used as an etching mask,whereby the gate electrode and the opposite electrode are patterned.Thereafter, the resist pattern RP3 may be removed. A hard mask may beformed by forming, e.g., a silicon nitride film under the resist patternRP3.

As illustrated in FIG. 4J, the extensions 5 and 7 are formed byion-implanting n-type impurities, such as As, (or p-type impurities,such as B, in the p-type cell) with the gate electrode 4 t (GE) and theopposite electrode 4 c (CE) used as masks. A p-type pocket region Pktsurrounding the n-type extension 5 may be formed by obliqueion-implanting p-type impurities, such as In, while the capacitor-sideextension 7 is covered with a resist mask. In the case of the p-typecell, an n-type pocket region may be formed by ion-implanting n-typeimpurities, such as P. The pocket region may be of the same conductivitytype as the well, and it may be omitted from some drawings. Ionimplantation may not be performed on the active region in the capacitorportion, which is covered with the opposite electrode CE. The implantedimpurities are activated by performing rapid thermal annealing (RTA) fora time period from a time not longer than 1 sec to about 15 sec oncondition that temperature is set to 900° C. to 1100° C.

As illustrated in FIG. 4K, an insulating film including silicon oxide orsilicon nitride and having a thickness of about 30 nm to 80 nm isdeposited on the semiconductor substrate so as to cover the gateelectrode 4 t and the opposite electrode 4 c. The extension 7 betweenthe gate electrode 4 t and the opposite electrode 4 c is covered with aresist pattern RP4. Anisotropic etching, such as reactive ion etching,is performed such that the sidewall spacer 6 t is left on the sidewallof the gate electrode 4 t on the bit line contact side thereof, and thatthe insulating film 6 c covering the capacitor-side extension 7 is left.Thereafter, the resist pattern RP4 may be removed. A known sidewallspacer, including a multilayer sidewall spacer, may be formed.

As illustrated in FIG. 4L, the bit line contact region BC having lowresistance is formed by masking the sidewall spacer 6 t and theinsulating film 6 c, and then ion-implanting n-type impurities, such asP, (or p-type impurities, such as B, in the p-type cell). An activationprocess may also be performed as required. After removing an oxide filmon the silicon surface, a Co film or a Ni film is formed on thesubstrate surface by sputtering, for example, and is changed to asilicide film with heat treatment. A silicide film 8 is formed bywashing out unreacted film portions and by performing the heat treatmentagain as required.

Thus, the memory cells are formed as illustrated in FIGS. 4A to 4L. Whenthe memory cells are integrated together with a CMOS logic circuit, theaccess transistors of the memory cells may be formed in processes commonto NMOS (or PMOS in the p-type cell) transistors of the logic circuit.The transistor and the capacitor are coupled to each other by a channelformed on the surface of the silicon substrate when a certain potentialis applied to the polysilicon layer (opposite electrode) 4 c that isformed in the capacitor region. Impurities may be implanted to thesurface of the silicon substrate in the capacitor region such that thesource and the drain of the transistor are electrically coupled to eachother. Thereafter, a lower interlayer insulating film may be formed soas to cover the memory cells and the MOS transistors of the logiccircuit. The structure illustrated in FIG. 2C may be formed by fillingan electrically conductive plug in the contact hole that has been formedby etching.

Multilayer wirings may be formed as disclosed in U.S. Pat. No.6,949,830, for example.

FIGS. 5A and 5B illustrate an exemplary memory cell array. FIG. 5A is aplan view of a memory cell array of the type using folded bit lines. Aplurality of elongate active regions AR are arrayed at a substantiallyconstant pitch in the vertical direction with the lengthwise directionof each active region being oriented in the horizontal direction. Theactive regions AR arrayed side by side in the vertical direction arearranged such that their positions are alternately shifted in the leftand right direction.

One active region AR includes a bit line contact region BC arranged at acenter and memory cells MC which are arranged on both the sides of thebit line contact region BC and each of which has a transistor (portion)Tr and a capacitor (portion) Cap. An opposite electrode CE is arrangedso as to overlap with respective parts of the active regions AR whilerespective ends of the active regions AR are left in a not-overlappedstate. The capacitor portions Cap are arrayed side by side in the columndirection with their positions in the row direction aligned with oneanother. The bit line contact regions BC are arranged to be alternatelylocated on the left side and the right side of the capacitor portionsCap. Transistor gate electrodes GE are arranged on both the sides of thebit line contact regions BC, thereby forming the transistors Tr in areaswhere the gate electrodes GE intersect the active regions AR.

FIG. 5B illustrates an exemplary memory cell region. Assuming that thewidth (gate length) of the gate electrode GE is L, the length of theoverlap between the opposite electrode CE and the active region AR is C,the pitch between the gate electrode GE and the opposite electrode CE isPP, the pitch between the center of the bit line contact region BC andthe gate electrode GE is PC, and the width of the active region AR andan element isolation width are each A, a cell area illustrated in FIGS.5A and 5B is expressed by the following formula:2A×(2PC+2PP+2L+C)  (1)

FIG. 6 illustrates an exemplary memory cell array. A region UA includesfour memory cell regions. Assuming that the pitch between the adjacentactive regions AR in different areas is CA, the length of the region UAin the vertical direction is expressed by (7A+CA) and the length of theregion UA in the horizontal direction is expressed by (PC+L+PP+C+A/2)based on the definition of the various lengths illustrated in FIG. 5B.Accordingly, a cell area is expressed by the following formula:(7A+CA)×(PC+L+PP+C+A/2)/4  (2)

The length (spacing) CA is longer than the pitch A between the adjacentactive regions AR in the area, for example, the element isolation width.An allowable amount by which the gate-electrode polysilicon layerprojects toward the word line contact region WC from the active regionAR positioned at the end of the area may be about A in consideration ofboth rounding of a distal end portion of the gate-electrode polysiliconlayer, which may be about A/2, and a positional deviation of the distalend portion, which is may be about A/2 together. The pitch between thegate-electrode polysilicon layers separated from each other may be aboutA. Further, in the first metal wiring on the upper layer, the lengthbetween the bit line and the first word auxiliary wiring may be about A.

The overlap between the wiring coupled to the word line contact regionWC and the coupled gate-electrode polysilicon layer may be about A/2,and the length between the wiring coupled to the word line contactregion WC and the not-coupled gate-electrode polysilicon layer may beabout the above-mentioned positional deviation, i.e., about A/2. Thelength CA may be about 3.5A.

A cell area of the memory cell, illustrated in FIG. 6, is expressed bythe following formula:2.625A×(PC+L+PP+C+A/2)  (2)′

The difference between the cell area of the memory cell illustrated inFIG. 5 and the cell area of the memory cell illustrated in FIG. 6 isexpressed by the following formula:1.375A×(PC+PP+L)−A×(0.625C+1.3125A)  (3)

Thus, the magnitude of the cell area may depend on the relationship inmagnitude between the added length of PC, PP and L and C.

In the case of A=0.1 μm, PC=0.1 μm, L=0.1 μm, PP=0.15 μm, and C=0.45 μm,for example, the cell area of the memory cell illustrated in FIG. 5 maybe 0.230 μm² and the cell area of the memory cell illustrated in FIG. 6may be 0.225 μm².

A twist structure may be employed, and the array of the bit lines,including the reference bit lines, may be changed.

FIG. 7 illustrates an exemplary bit line array. In FIG. 7, the bit linearray illustrated in FIG. 1C is represented on the left side of a twistportion TW, i.e., on the sense amplifier side, and cross-wiring isperformed in the twist portion TW to provide a bit line arrayrepresented on the right side of the twist portion TW.

In the bit line array illustrated in FIG. 1C, for example, on the leftside of the twist portion TW, the bit line BL1 may be adjacent to thereference bit line /BL1. Because the reference bit line generates nonoise, noise generated in the bit line BL1 may be reduced. Because thebit line BL2, for example, is adjacent to the other bit lines BL1 andBL3, noise generated in the bit line BL2 may not be reduced.

Through the twist structure, the bit line BL2 is made adjacent to boththe reference bit line /BL2 and the reference bit line /BL1 on the rightside of the twist portion TW. The reference bit line /BL2 may generateno noise. The bit line BL2 is adjacent to the bit line BL1 and thereference bit line /BL1 on the left side and the right side of the twistportion TW, respectively. Because noises are generated in the bit lineBL1 and the reference bit line /BL1 in opposed directions, those noisesmay be cancelled.

In the bit line array illustrated in FIG. 1C, for example, on the leftside of the twist portion TW, the word line contact regions WC arearranged between the bit line BL1 and the reference bit line /BL1, orbetween the bit line BL4 and the reference bit line /BL4. The word linecontact regions WC may be not arranged between the bit line BL2 and thereference bit line /BL2, or between the bit line BL3 and the referencebit line /BL3.

On the right side of the twist portion TW, the word line contact regionsWC are arranged between the bit line BL2 and the reference bit line/BL2, or between the bit line BL3 and the reference bit line /BL3.Through the twist structure, the pair of bit line and reference bit lineadjacent to each other in a sandwiching relation with respect to theword line contact regions WC may be replaced by another pair. Noises inthe sensing operation may be reduced in the bit line and the referencebit line, which adjacent to each other in a sandwiching relation withrespect to the word line contact regions WC, as illustrated in FIG. 1C.

FIGS. 8A and 8B illustrate an exemplary memory cell array. FIG. 8A is aplan view of the memory cell array. Each active region AR may have ashape bent at both end ends thereof. Each active region AR illustratedin FIG. 2A has a shape extending straightforward in the horizontaldirection. In FIG. 2A, there is a wide area under the opposite electrodeCE between the active regions AR which are adjacent to each other, butthey belong to different areas. The array efficiency of the capacitorportions may be increased by forming active regions in such a wide area.

In FIG. 8A, four active regions AR are arrayed side by side at asubstantially constant pitch in the vertical direction within the areain a portion where the active regions AR extend horizontally. The pitchbetween the adjacent active regions AR belonging to different areas maybe wide enough to arrange the word line contact regions WC in thatpitch.

A right end portion of each active region AR is bent downwards as viewedon the drawing, and a left end portion of each active region AR is bentupwards as viewed on the drawing. A portion of the active region ARranging from its bent point to its end may be referenced as a “bentportion BP”. The bent portion BP extends under the opposite electrodeCE. Under the opposite electrode CE, the bent portions BP of the activeregions AR are arrayed at a substantially constant pitch parallel to oneanother in a direction perpendicular to the direction in which the bentportions BP extend. A column of the active regions AR may be arrangedsuch that their horizontal positions, e.g., respective ends of the bentportions, are aligned with one another. A row of the active regions ARmay be arranged such that vertical positions of their horizontallyextending positions are aligned with one another.

An angle at which each bent portion BP is bent from the horizontaldirection may be larger than 0°, but smaller than 90°. For example, thebent angle may be in the range of about 30° to 50°. The direction inwhich each bent portion BP extends may differ from the horizontaldirection and the vertical direction. Respective horizontal positions ofthe bent points are shifted for each active region AR such that the bentportions BP are arrayed at a substantially constant pitch under theopposite electrode CE. Accordingly, the capacitor portions may bearrayed at a minimum pitch, for example.

FIG. 8B illustrates the memory cell of the memory cell array illustratedin FIG. 8A. Assuming, for example, that the width of the gate electrodeGE, i.e., the gate length, is L, the length of the overlap between theopposite electrode CE and the active region AR (at its center in thewidthwise direction) is C, the pitch between the gate electrode GE andthe opposite electrode CE is PP, the pitch between the center of the bitline contact region BC and the gate electrode GE is PC, the width of theactive region AR under the opposite electrode CE and the elementisolation width are each A, the pitch between the active region ARadjacent to each other in the lengthwise direction thereof under theopposite electrode CE is AA, and the bent angle is 45°, a cell area isexpressed by the following formula:2A×(√2(PC+L+PP)+C+AA/2)  (4)

In the case of A=0.1 μm, AA=0.1 μm, PC=0.1 μm, L=0.1 μm, PP=0.15 μm, andC=0.45 μm, for example, the cell area may be 0.199 μm².

The number of access transistors sharing the gate electrode, e.g., thenumber of memory cells arrayed side by side in the vertical directionwithin one area, may be arbitrarily selected.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the invention andthe concepts contributed by the inventor to furthering the art, and areto be construed as being without limitation to such specifically recitedexamples and conditions. Although the embodiment(s) of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A semiconductor storage device comprising: a semiconductor substrate;a plurality of memory cells formed on the semiconductor substrate, eachof the plurality of memory cells including a transistor and a capacitor;a plurality of bit lines extending in a first direction; a plurality ofword lines extending in a second direction which is different from thefirst direction; and a plurality of sense amplifiers including a firstsense amplifier and a second sense amplifier, wherein the plurality ofmemory cells includes: a first memory cell group sharing a firstauxiliary word line; and a second memory cell group sharing a secondauxiliary word line, wherein the plurality of word lines includes afirst word line coupled to the first auxiliary word line and a secondword line coupled to the second auxiliary word line, the first word lineis coupled to the first auxiliary word line in a first word line contactregion, the second word line is coupled to the second auxiliary wordline in a second word line contact region, the plurality of bit linesincludes a first bit line and a second bit line respectively provided onboth sides of the first word line contact region, and the first bit lineand the second bit line are coupled to the first sense amplifier.
 2. Thesemiconductor storage device according to claim 1, wherein the firstauxiliary word line includes a first gate electrode corresponding to atransistor included in at least one of the plurality of memory cells,and the second auxiliary word line includes a second gate electrodecorresponding to a transistor included in at least one of the pluralityof memory cells.
 3. The semiconductor storage device according to claim1, wherein the transistor includes a first diffusion region and a seconddiffusion region which are formed below both sides of the gate electroderespectively, the first diffusion region includes a bit line contactregion coupled to one of the plurality of bit lines, and the seconddiffusion region is coupled to the capacitor.
 4. The semiconductorstorage device according to claim 1, further comprising: a plurality offirst regions which extend in the first direction and are arranged at apredetermined spacing in the second direction in the first memory cellgroup and the second memory cell group, wherein a first spacing betweenthe first regions adjacent to each other in the second direction in oneof the first memory cell group and the second memory cell group isshorter than a second spacing between the first regions which areadjacent to each other in the second direction and belong to one of thefirst memory cell group and the second memory cell group, respectively.5. The semiconductor storage device according to claim 3, furthercomprising: an element isolation region surrounding the first diffusionregion and the second diffusion region, wherein the capacitor is formedin a portion of the element isolation region, which includes an exposedsidewall of an active region.
 6. The semiconductor storage deviceaccording to claim 3, further comprising a third memory cell groupincluded in the plurality of memory cells which shares a third auxiliaryword line extending in the second direction and sharing as gateelectrodes of the transistors, wherein the plurality of word linesinclude a third word line coupled to the third auxiliary word line, thethird word line is coupled to the third auxiliary word line in a thirdword line contact region, the first memory cell group is arranged on oneside of the bit line contact region and the third memory cell group isarranged on the other side of the bit line contact region, the firstword line contact region is arranged in the second direction at one endof the first auxiliary word line or the third auxiliary word line, andthe third word line contact region is arranged in the second directionat an opposite end of the first auxiliary word line or the thirdauxiliary word line.
 7. The semiconductor storage device according toclaim 1, further comprising: a third bit line and a fourth bit linewhich are included in the plurality of bit lines and are coupled to thesecond sense amplifier; a second region where the third bit line and thefourth bit line are not adjacent each other; and a third region where athird word line contact region is provided between the third bit lineand the fourth bit line.
 8. The semiconductor storage device accordingto claim 3, further comprising a plurality of first regions which extendin the first direction and are arranged at a predetermined spacing inthe second direction within each of the first memory cell group and thesecond memory cell group, wherein the capacitor includes an oppositeelectrode, and an active region including the first diffusion region andthe second diffusion region includes a fourth region which is bent fromthe first region and is arranged under the opposite electrode.
 9. Thesemiconductor storage device according to claim 8, wherein a bentposition of the fourth region differs for each of active regions thatare arrayed side by side in the second direction within the first memorycell group and includes the first diffusion region and the seconddiffusion region.
 10. The semiconductor storage device according toclaim 8, wherein the fourth regions are arranged at a predeterminedspacing under the opposite electrode.
 11. The semiconductor storagedevice according to claim 1, wherein four of the plurality of bit linesare coupled to the first memory cell group, and four of the plurality ofbit lines are coupled to the second memory cell group.
 12. Thesemiconductor storage device according to claim 1, further comprising: afirst wiring layer from which the plurality of bit lines are formed; asecond wiring layer formed over the first wiring layer; a word auxiliarywiring formed from the second wiring layer and coupled to the gateelectrode; and a third wiring layer which is formed over the secondwiring layer and from which the word line coupled to the word auxiliarywiring is formed.